1. Field of the Invention
This invention relates to the dynamic measurement of optical wavefronts and more particularly to the real-time measurement of a temporally varying optical wavefront.
2. Description of the Related Art
There are many applications for adaptive optics systems. Optical propagation through the atmosphere can distort wavefronts. This can cause loss of information during digital transmission in optical communications. In imaging applications, such as ground based astronomy, it can lead to loss of fidelity and resolution. Manufacturing applications such as laser cutting or welding implement adaptive optics for precise control of optical energy deposition geometry.
All adaptive optics systems are basically composed of three subassemblies—a wavefront sensor, an electronic wavefront processor and an active wavefront corrector. Advances have been made on the latter two subassemblies. However, wavefront measurements are still accomplished by some means of self-measurement, such as interferometry or holography. Interferometric and holographic means work well in settings where there are strict measurements environment constraints. However, they are very sensitive to alignment and mechanical instabilities. This indicates that their utility is limited in applications where mechanical vibrations are inherent. A technique is needed to minimize these stability problems.
K. Buse and M. Luennemann, in their article entitled, 3D Imaging: Wave Front Sensing Utilizing a Birefringent Crystal, (Physical Review Letters, Vol 85, No 16, Pgs 3385-3387, Oct. 16, 2000) disclose the measurement of a wavefront utilizing a rotatable thin birefringent crystal and two polarizers. In their experiments, phase-front distortions, as small as 15 μm, are detected with a dynamic range of 3 mm and a spatial resolution of 50 μm. Such a dynamic range in spatial resolution exceeds the performance of conventional wavefront sensors of, for example, the Shack-Hartmann type.
However, use of a birefringent crystal, does not allow for the capability of providing real-time monitoring. Specifically, the Buse/Luennemann implementation calls for the mechanical rotation of the crystal in order to measure any given wavefront. Any wavefront that has a temporal dependence (e.g. one that is being modulated by atmospheric fluctuations) could not be measured this way.